A light scanning unit scans light emitted from a light source over an area, and is in wide usage, for example, in electrophotographic image forming apparatuses and in scan display devices.
In an image forming apparatus, the scanned light is utilized in the image formation, and thus determining the starting and ending positions of the light scanning is important for the proper formation of the image. A light scanning unit thus generally includes a synchronization signal detection unit for adjusting the horizontal synchronization of the image.
For example, in an electrophotographic image forming apparatus, the light scanning unit scans a light beam onto select portions of a uniformly charged surface of a photosensitive drum to thereby form an electrostatic latent image as the resulting potential difference, which is later developed using a developing agent such as, for example, toner, into a visible image. So developed visible image is then transferred onto a printing medium. If the scanning position of the light beam between scanning lines on the photosensitive drum of the above described image forming apparatus were to shift or vary, corresponding shifting in the image lines results; and, particularly when forming a color image, misalignments between the overlapping of the individual color images may occur, in turn resulting in blurred color image that may appear out of focus. The synchronization signal detection unit of the light scanning unit detects a portion of the scanned light beam in order to determine the proper scanning position of the scanned light beam. It is thus desirable to reduce the noise in the synchronization signal detection unit, particularly when forming a high resolution image.